JP2000247490A - Sheet carrying device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To curl various kinds of sheet with a simple configuration by provid ing a pair of rollers which is stopped at a time while a tip of sheet is held by nip portions of the pair. SOLUTION: A pair of opposite rollers 66, 67 is made of rubbery elastic body having a lower hadness than that of a registration roller 65 and has a recessed shape at their portions abutting on the outer periphery of the roller 65. According to the advance angle of a sheet to nip portions of the registration roller 65 and the opposite roller 66 after it passes through guide plates 63, 64, the sheet has a curled portion proturding rightward. Sheet detection sensors 68, 69 detecting the advance of sheet to a registration means 60 detects generation of drive control timming of the registration means 60 and the sheet conveyed. Accordingly, the sheet is corrected in its posture and is adjusted in its timming to the sucked by a transfer drum by the registration means 60, and then has a curled portion along the outer periphery of the transfer drum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying apparatus for conveying various types of sheet materials having different materials and thicknesses, and an image forming apparatus capable of forming an image on the sheet material.

[0002]

2. Description of the Related Art For example, in an example of a color image forming apparatus using an electrophotographic system, a toner image formed on a photosensitive drum is transferred for each color to a transfer drum having a sheet-like sheet material carried on an outer peripheral surface. After that, there is a method which employs a method of fixing a toner to a sheet material using a fixing device having a heating means such as a heat roller and forming an image.

In order to form a high-quality image using various sheet materials in this image forming apparatus, it is necessary to control the curling of the sheet material, to control the variable fixing speed, and to form the image before the sheet material is carried on the transfer drum. The image forming control is performed by setting and responding to a high-voltage output value and timing control for each sheet material.

[0004]

However, with respect to the conventional curling control of the sheet material, especially when the electrostatic attraction is adopted as the sheet material holding means of the transfer drum,
Necessary as an auxiliary means of electrostatic attraction to ensure that various sheet materials (the stiffness (flexibility) varies depending on the thickness and material of the sheet material, etc.) on the outer surface of the transfer drum It is necessary to change the curling amount or curling ability for the sheet material according to the type of the sheet material.

In order to realize this, the function of varying the curling amount of the sheet material curling means (for example,
In the case of a configuration in which curling is performed by passing through the nip of two roller pairs of an elastic roller and a hard roller, a function of changing the curling amount by changing the interval between the roller pairs must be employed. The mechanical device configuration has become complicated, leading to an increase in cost.

In the case of a configuration in which various types of sheet materials are fed from a plurality of paper feed units, it is necessary to arrange sheet material curling means in correspondence with each of the transport paths from each paper feed unit. , Had a more complex configuration.

An object of the present invention is to solve the above-mentioned problems of the prior art. It is an object of the present invention to provide a sheet material capable of appropriately controlling curling of various types of sheet materials with a simple configuration. An object of the present invention is to provide a transport device and an image forming apparatus.

[0008]

In order to achieve the above object, according to the present invention, the sheet material is conveyed, and the sheet material is pinched and conveyed at a nip portion in the conveyance path to enable curling. A roller pair, and control means for controlling the drive of the roller pair, wherein the control means temporarily stops the roller pair in a state where the leading end of the sheet material is held in the nip portion of the roller pair. Features.

[0009] The control means tilts the leading end of the sheet material conveyed by the conveying means disposed upstream of the roller pair in the conveying path against the nip portion of the stopped roller pair. After performing the line correction, it is also preferable to drive the roller pair to guide the sheet material to the nip portion.

[0010] It is also preferable that the control means adjusts the timing of conveying the sheet material to the downstream side of the pair of rollers in the conveying path.

[0011] Sheet material information input means for inputting sheet material type information as one of the control information of the control means, the control means comprising a nip for the roller pair in accordance with the input sheet material type information. It is also preferable that it is possible to selectively control whether or not to temporarily stop the roller pair in a state where the leading end of the sheet material is held between the portions.

[0012] An image forming apparatus is provided with the sheet material conveying device described above, and image forming means for forming an image on the sheet material conveyed by the sheet material conveying device.

It is also preferable that the image forming means has a holding means for electrostatically adsorbing the conveyed sheet material and to carry the sheet material on a surface thereof, and to form a toner image on the sheet material carried on the surface of the carrying means. It is.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIG. 1 shows a color image forming apparatus (image forming apparatus PR) according to a first embodiment.
FIG. 1 shows a schematic sectional configuration explanatory diagram of 1). In this example, a digital color image reader unit 201 (hereinafter, “reader unit”)
), And a digital color image printer unit 202
(Hereinafter abbreviated as “printer unit”), an image processing unit 203 is provided between the reader unit 201 and the printer unit 202.

First, a schematic configuration of the image forming apparatus PR1 will be described below.

In the reader unit 201, the original 30 is placed on an original table glass 31 and is exposed and scanned by an exposure lamp 32, so that a reflected light image from the original 30 is
3, the light is condensed on the full color sensor 34 integrally formed with the RGB three-color separation filter, and a color-separated image analog signal is obtained.

The color-separated image analog signal is digitized through an amplifier circuit (not shown), processed by an image processing unit 203, and sent to a printer unit 202.

In the printer unit 202, a photosensitive drum 1 as an image carrier is rotatably supported in the direction of an arrow. Around the photosensitive drum 1, a pre-exposure lamp 11, a corona charger 2, a laser exposure optical system 3 , A potential sensor 12, a developing device 4 (developing units 4y, 4c, 4m, and 4Bk), a drum light amount detection sensor 13, a transfer device 5, and a cleaning device 6.

In the laser exposure optical system 3, the reader unit 2
The image signal from 01 is converted into an optical signal by a laser output unit (not shown), and the converted laser light is reflected by a polygon mirror 3a, passes through a lens 3b and a mirror 3c,
The image is projected on the surface of the photosensitive drum 1.

When an image is formed by the printer unit 202,
The photosensitive drum 1 is rotated in the direction of the arrow, and the pre-exposure lamp 11 is rotated.
After the photosensitive drum 1 is neutralized by the corona charger 2, the latent image is formed by irradiating a light image E for each separation color.

Next, a predetermined developing device is operated to develop the latent image on the photosensitive drum 1 to form a toner image on the photosensitive drum 1 using a resin as a base. The developer is an eccentric cam 2
The operation of 4y, 24c, 24m, and 24Bk causes the photosensitive drum 1 to be brought closer to the photosensitive drum 1 in accordance with each separation color.

The developed toner image on the photosensitive drum 1 is stored in a sheet material cassette 7a, 7b, 7c, an intermediate tray 2
2 or from a sheet material tray 7m capable of manual sheet feeding, to a sheet material supplied to a position facing the photosensitive drum 1 via a transport system and a transfer device 5.

The transfer device 5 of this embodiment includes a transfer drum 5a as a sheet material holding means, a transfer charger 5b, a suction port 5g opposed to a suction charger 5c for electrostatically sucking the sheet material, a suction operation. For this purpose, the transfer drum 5a has an inner charger 5d and an outer charger 5e for removing charges from the transfer drum 5a. A sheet material carrying sheet 5f is integrally stretched in a cylindrical shape. As the sheet material carrying sheet 5f, a dielectric sheet such as a polycarbonate film is used (hereinafter, referred to as "transfer sheet 5f").

As the drum-shaped transfer device, that is, the transfer drum 5a is rotated, the toner image on the photosensitive drum is transferred onto the sheet carried on the carrier sheet 5f by the transfer charger 5b. Thus, a desired number of color images are transferred to the sheet material suction-conveyed to the transfer sheet 5f, and a full-color image is formed.

In the case of forming a full-color image, when the transfer of the toner images of four colors is completed in this way, the sheet material is separated from the transfer drum 5a by the action of the separation claw 8a, the separation push-up roller 8b and the separation charger 5h, and fixed. The paper is discharged onto a tray 10 via a container 9 (heat roller fixing device). Alternatively, after the sheet material is sent to a post-discharge post-processing unit 600 described later, post-processing such as desired collation and stapling is performed.

On the other hand, the post-transfer photosensitive drum 1 is subjected to the image forming process again after the residual toner on the surface is cleaned by the cleaning device 6.

When images are formed on both sides of the sheet material, the sheet material is discharged from the fixing unit 9 and immediately after that, the conveyance path switching guide 19 is driven, and once guided to the reversing path 21a via the conveyance vertical path 20. Then, due to the reverse rotation of the reversing roller 21 b, the sheet is retracted in a direction opposite to the direction in which the sheet is fed, with the rear end of the sheet being fed, and stored in the intermediate tray 22. Thereafter, an image is formed on the other surface again by the above-described image forming step.

When an image is formed on both the front and back surfaces of the sheet material, the first surface of the sheet material on which the image is formed first is referred to as the "first surface of both surfaces", and then the second surface on which the image is formed is formed. The surface is referred to as the “second surface of both surfaces”.

In order to prevent the powder from scattering and adhering to the transfer sheet 5f of the transfer drum 5a and the oil to be described later adhering to the sheet material, the transfer drum 5a has a fur opposed to the transfer drum 5a via the transfer sheet 5f. Brush 14 and fur backup brush 15, oil cleaning roller 16 and oil cleaning backup brush 17 facing each other via transfer sheet 5f, polishing roller 18 and polishing roller backup brush 18 facing each other via transfer sheet 5f.
Cleaning is performed by a or the like. Such cleaning is performed before or after image formation, and at any time when a jam (paper jam) occurs.

In this embodiment, the eccentric cam 25 is operated at a desired timing, and the cam follower 5i integrated with the transfer drum 5a is operated, so that the gap between the supporting sheet 5f and the photosensitive drum 1 can be arbitrarily set. It has a configuration that can be set. For example, the interval between the transfer drum 5a and the photosensitive drum 1 can be increased during standby or when the power is off.

FIG. 2 is a block diagram of a control system in the image forming apparatus PR1. The color image forming apparatus is roughly divided into two blocks for control. One is a reader controller 700 that mainly controls the reader unit 201 and the image processing unit 203, and the other is the printer unit 2.
02 is a printer controller 701 that controls the printer.

Reference numeral 702 denotes scanning mirrors 32a, 32b, 3
2c and an optical motor driver for driving an optical motor (not shown) for moving the exposure lamp 32 (see FIG. 1);
03 is an automatic document feeder RD for automatically exchanging documents.
RDF controller for controlling F400, 704
Is an operation unit for setting an operation mode of the color image forming apparatus, 705 is a ROM storing a control program of the reader controller 700, 706 is a RAM storing data such as control values, 707 is a halo lamp 32, etc. This is an I / O for driving a load. Also, RAM 706
Is backed up by a battery so that data can be retained even when the power is turned off.

Next, the peripheral control unit of the printer controller 701 will be described. A ROM 750 stores a control program of the printer controller 701, and a RAM 751 stores data such as control values.

The A / D converter 752 includes a developer udon detector 780, an upper fixing thermistor 781, a lower fixing thermistor 782, a potential sensor 12, a temperature sensor 783, a humidity sensor 784, a density detection sensor 785 on the surface of the photosensitive drum,
A D / A converter 753 for converting an analog signal from the on-drum light amount detection sensor 13 or the like to digital data outputs an analog set value to the high voltage control unit 770 or the like, and a 754 drives loads such as motors and clutches. I / O.

The I / O 754 inputs and outputs control information with the photosensitive drum motor driver 760, the fixing drive motor driver 761, the main motor driver 762, the curl motor driver 763, and the like.

The curl motor driver 763 drives a curl motor or an eccentric cam motor which is a driving source of a curl correction unit 500 for removing a curl on a sheet material on which an image is formed, which will be described later.

Reference numeral 708 denotes a sorter controller which communicates with the printer controller 701 and controls the stacking according to the stacking mode instruction set in the non-sort mode, the sort mode or the group mode set by the operation unit 704, or the stapling instruction. Staple control is performed.

FIG. 3 is a block diagram showing a configuration example of the image processing section 203 in the present embodiment. In FIG. 3, reference numeral 101 denotes a CCD reading unit, which is an amplifier for amplifying the analog RGB signals input from the above-described full-color sensor 34 (see FIG. 1), and for converting the analog RGB signals into, for example, 8-bit digital signals. A
A / D converter, a known shading correction circuit for performing shading correction, and the like output a digital RGB image signal of a document image.

Reference numeral 102 denotes a shift memory, which receives a CC signal in response to a shift amount control signal from the reader controller 700.
For example, a shift between colors and between pixels of the RGB image signal input from the D reading unit 101 is corrected.

Reference numeral 103 denotes a complementary color conversion circuit which converts an RGB image signal input from the shift memory 102 into an MCY image signal. Reference numeral 104 denotes a black extraction circuit which extracts a black area of an image from an MCY (magenta, cyan, yellow) image signal input from the complementary color conversion circuit 103 in accordance with a black extraction signal input from the reader controller 700. A Bk (black) image signal for the black region is output.

Reference numeral 105 denotes a UCR circuit, which is a black extraction circuit 1
The MCY image signal input from the complementary color conversion circuit 103 is subjected to under color removal (UCR) processing according to the Bk image signal input from the input device 04 and the UCR amount control signal input from the reader controller 700. That is, the black extraction circuit 10
4 and the UCR circuit 105 convert the extracted black area into MCY3
FIG. 26 shows an improvement in color reproducibility by forming an image by replacing the color toner with the Bk toner instead of superimposing the color toner.

The Bk image signal output from the black extraction circuit 104 is determined by equation (1).

[0044]

BK = A · min (C2, Y2, M2) In Equation 1, A is a black extraction coefficient, C2, Y2,
M2 is an MCY image signal output from the complementary color conversion circuit 103. The black extraction coefficient A is determined by the reader controller 700
Is determined by a black extraction amount control signal designated by

Also, M output from UCR circuit 105
The CY image signal is determined by Equation 2.

[0046]

M1 = B1 · (M2-D1 · Bk) Cl = B2 · (C2−D2 · Bk) Y1 = B3 · (Y2−D3 · Bk) where M2, C2 and Y2 are complementary color conversions. MCY image signal output from the circuit 103, Ml, Cl, Y
1 is an MCY image signal output from the UCR circuit 105, and the coefficients B1, B2, B3, D1, D2, and D3 are determined by the UCR amount control signal from the reader controller 700.

Reference numeral 106 denotes a masking circuit, which is a reader controller 700 for removing turbid components of the toner to be used and correcting the RGB filter characteristics of the CCD.
UC according to the masking coefficient control signal input from
A masking process is performed on the MCY image signal input from the R circuit 105.

MC output from masking circuit 106
The Y image signal is represented by Expression 3.

[0049]

| M0 | | a11 a12 a13 || M1 || Y0 | = | a21 a22 a23 || Y1 || C0 || a31 a32 a33 || C1 | In Formula 3, all to a33 are masking coefficients. ,
Ml, Cl, and Yl are Ms output from the UCR circuit 105.
The CY image signal, M0, C0, Y0 is a masking circuit 10
6 is an MCY image signal, and the masking coefficients all to a33 are determined by a masking coefficient control signal specified by the reader controller 700.

Reference numeral 107 denotes a selector, which outputs M, C, Y, and Bk image signals input from the masking circuit 106 and the black extraction circuit 104 in accordance with the color selection signal input from the reader controller 700 to the color selection terminal S1. And selects one color image signal to output the image signal Vl.

Reference numeral 108 denotes a reader gradation correction circuit which performs gradation correction as shown in FIG. 4 on the image signal V1 input from the selector 107 and outputs an image signal V2. For example, the reader gradation correction circuit 108
The density correction is performed on the image signal according to one of the conversion characteristics a to e in FIG. 4 selected based on the tone correction selection signal designated from 00.

The setting in the reader gradation correction circuit 108 is determined by the image density setting of the operation unit described later. This is set to the terminal S3 of the reader gradation correction circuit 108. Further, since these density corrections may be different for each color, the same setting as the above-mentioned color selection terminal S1 is applied to the circuit 10.
8 is set to the color selection terminal S2, and the selected density-corrected signal for the selected color is output as V2.

Reference numeral 109 denotes a printer gradation correction circuit, which performs gamma conversion shown in FIG. 5 according to a printer color selection signal input from the printer controller 701 in order to make the output characteristics of the printer unit 202 linear for each color. One of the characteristics M, C, Y, and bk is selected and set to the color selection terminal S4 to correct the image signal.

Reference numeral 110 denotes a laser driver which controls the laser exposure optical system 3 (see FIG. 1). The laser driver 110 modulates the semiconductor laser based on the image signal V3 input from the printer gradation correction image path 109. When driven, a latent image is formed on the photosensitive drum 1.

FIG. 6 shows the operation unit 704 of the color image forming apparatus of the present invention. In FIG. 6, reference numeral 351 denotes a numeric keypad which is used for setting the number of images to be formed and for inputting numerical values for mode setting. Reference numeral 352 denotes a clear / stop key, which is used to stop the set number of images to be formed and the image forming operation.

A reset key 353 is used to return a set number of images to be formed, an operation mode, and a mode such as a selected paper feed stage to a specified value. A start key 354 starts an image forming operation by pressing the start key.

Reference numeral 369 denotes a display panel composed of a liquid crystal or the like, and the display content changes according to the setting mode in order to facilitate detailed mode setting. In the present embodiment, the cursor on the display panel 369 is moved with the cursor keys 365 to 368, and the setting is determined with the OK key 364. Such a setting method can be configured by a touch panel.

A paper type setting key 371 is set when an image is formed on a sheet material thicker than a standard or various sheet materials such as OHP. A paper type selection screen is displayed on the display panel 369 by the paper type setting key 371, and the sheet type is selected by the cursor keys 365 to 368, but the setting screen is omitted from the description.

When the thick paper mode, which is frequently set, is set, the LED 370 is controlled to light up. In other settings, the LED 370 is controlled so as not to light.
In the present embodiment, only the thick paper mode can be set, but the function can be extended so that the mode of the OHP or other special sheet material can be set as necessary.

Reference numeral 375 denotes a double-sided mode setting key. For example, a "single-sided mode" for performing single-sided output from a single-sided original, a "single-sided mode" for performing double-sided output from a single-sided original, and a "double-sided output for performing double-sided output from a double-sided original" Two-sided mode "-2 from double-sided original
It is possible to set four types of two-sided mode, that is, a "two-sided mode" for outputting one side of a sheet.

The LEDs 372 to 374 are turned on in accordance with the set double-sided mode, and in the "single-single mode", the LEDs 37 to 374 are turned on.
2 to 374 are all turned off, and in “one-sided mode”, LE
Only D372 lights up, LED37 in "both-both mode"
Only the LED 374 is turned on, and only the LED 374 is turned on in the “both-single mode”.

Reference numerals 300, 301, 302, and 303 denote magnification setting keys, reference numerals 304 and 305 denote manual density adjustment setting keys, and reference numeral 307 denotes a display section for manually setting density values.

In this embodiment, since the electrostatic attraction means is used to attract the surface of the transfer drum 5a as the sheet material holding means, the sheet material (250 mm or less) of the entire circumference of the transfer sheet 5f is used. In the case of (2), images can be formed on two sheet materials at the same time. The case where the two sheet materials are simultaneously image-formed is hereinafter referred to as “two-sheet sticking control”, and the case where one sheet material is electrostatically attracted to the transfer sheet 5f to form an image is referred to as “one-sheet sticking control”. "

FIG. 7A shows a state in which one sheet material is adsorbed when one sheet is adhered to the transfer drum 5a. FIG. 7B shows a state in which two sheets are adhered to the transfer drum 5a and the sheet material is attracted. The sheet material when one sheet is stuck is adsorbed at the fixed point PTA on the transfer drum 5a at the top, and even if the size of the sheet material in the rotation direction of the transfer drum is changed, control is performed so that the astigmatism is adsorbed to the fixed point PTA ( Adsorption form of sheet material A).

On the other hand, when two sheets are adhered, similarly, the fixed point PTA is adsorbed so as to be the leading end (adsorption mode of the sheet material B), and the second sheet is a point 180 ° opposite to the transfer drum at the fixed point PTA. The sheet material C is adsorbed so that the fixed point PTB is at the tip (adsorption form of the sheet material C).

In the case of sticking two sheets, as in the case of sticking one sheet, even if the sheet material size changes, the sheet is sucked so that the fixed points PTA and PTB are at the leading ends. Although not shown in FIG. 1, in any case, the suction is performed so as to avoid the connecting portion 5z for realizing the connection of the transfer sheets 5f.

The control for adsorbing the sheet material so that the leading end of the sheet material comes first at the fixed point PTA will be referred to as A-side suction or A-side sticking control, and the control for sucking the sheet material at the fixed point PTB will be referred to as B-side suction or B-side sticking control. I will express it.

The transfer drum reference signal for controlling the image forming operation will be described with reference to FIG. A sensor (not shown) and a sensor detection flag are arranged in the transfer drum 5a in order to match the formed image with the sheet material adsorbed on the transfer drum 5a such that the fixed point PTA is at the top.

Specifically, FIG. 8 shows a state of the photosensitive drum 1 and the transfer drum 5a immediately after the start of the latent image formation, and shows a state where the leading end of the latent image overlaps the leading end of the sheet material at the transfer position.

On the other hand, FIG. 9 shows the relationship between the latent image (laser), the reading operation of the reader unit 201, and the transfer drum reference signal A. The transfer is performed Tprei time before the start timing of the latent image formation. The drum reference signal A is arranged so as to fall.

The reader unit 201 controls the scanning mirror 3a of the laser exposure optical system 3 from the fall of the transfer drum reference signal A (hereinafter referred to as ITOP-A) to a speed required for a predetermined magnification within the time Tprei within the achievable reading magnification. The running time or distance required for startup and vibration absorption can be secured. A similar signal is also prepared for the B-side control, and this signal is used as a transfer drum reference signal B (hereinafter referred to as IT).
OP-B).

These transfer drum reference signals are supplied when the transfer drum 5a is rotating, that is, the eccentric cam 24 is operated, and the photosensitive drum 1 is driven by the photosensitive drum motor driver 76.
This is generated when operating at 0.
As a result, during the operation of the eccentric cam 24, the transfer drum 5a rotates at the same speed as the photosensitive drum 1.

As will be described later, the photosensitive drum motor is also formed so as to be driven at a plurality of different speeds in a form corresponding to the fixing speed.

Next, the toner density control in the developing device 4 will be described. Each toner in the magenta developing device 4m, cyan developing device 4c and yellow developing device 4y reflects near-infrared light having a wavelength of about 960 nm. The reflected light is detected by a developer concentration detecting section 780 (see FIG. 2) disposed in the inside, and is converted into a toner concentration signal by an A / D converter 752 (see FIG. 2). The developer is supplied from a hopper (not shown).

On the other hand, black toner has a wavelength of about 96
Since the near infrared light of 0 nm is absorbed, the toner concentration is not detected in the black developing device 4Bk, and the photosensitive drum 1 is not detected.
Wavelength of about 960 for the black toner image developed above
irradiating near-infrared light of about nm, the ratio of the reflection component on the surface of the photosensitive drum 1 and the absorption component of the black toner is detected by the on-drum light amount detection sensor 13 and converted by the A / D converter 752 (see FIG. 2) Then, the black toner density is detected from the developed toner image density, and the toner density in the developing device is calculated based on the black toner density.

The on-drum light amount detection sensor 13 is disposed between the black developing device 4Bk and the transfer charger 5b, and has a horizontal structure capable of detecting a toner image developed by the developing device before transfer.

Next, the heat roller fixing device 9 will be described in detail. Heat roller fixing device 9. Upper fixing roller 9a, lower fixing roller 9b, fixing web 9c, fixing oil application roller 9
d.

The hot-roller fixing unit 9 is provided with a fixing upper / lower roller 9.
The toner on the sheet material is melted by the heat energy of a and 9b, and the fused toner and the sheet material are fixed by the pressure between the upper and lower fixing rollers 9a and 9b. The surfaces of the upper fixing roller 9a and the lower fixing roller 9b are fixed to the upper central fixing heater 9e,
And an upper fixing thermistor 781 and a lower fixing thermistor 782 (see FIG. 2) that detect the respective roller surface temperatures are controlled so as to obtain an optimum surface temperature independently.

The fixing web 9c comes into contact with the fixing upper opening 9a when necessary in order to remove dirt or offset toner on the fixing upper opening 9a. At this time, a new surface of the fixing web 9c is brought into contact with the upper fixing roller 9a by a winding device incorporated in the fixing web 9c, so that the cleaning performance can be improved. The fixing oil application port 9 supplies silicone oil to the surface of the cleaned upper fixing roller 9a.
d is prepared, and silicone oil is applied to the upper fixing roller 9a when necessary so that the toner on the sheet material does not adhere to the upper fixing roller 9a.

Further, the hot-roller fixing device 9 is driven by a fixing driving motor (not shown in FIG. 1) to fix upper / lower rollers 9a, 9b.
Then, the sheet material conveying section 9g is driven. The fixing drive motor is driven by a fixing drive motor driver 761 (see FIG. 2). In the present embodiment, in order to eliminate the difference in the fixing property depending on the type of the sheet material, the sheet is horizontally formed so as to realize the fixing speed corresponding to the four types of sheet materials.

Assuming that the specific peripheral speed of the photosensitive drum 1 during image formation is VP (hereinafter referred to as “process speed”), the fixing speed VFN of plain paper is VP, and the fixing speed VFD for the second side of both sides is VFN. The fixing speed VFT for thick paper is smaller than VFD, and the fixing speed VFO for OHP is smaller than VFT. Therefore, VP
= VFN>VFD>VFT> VFO, and the fixing drive motor driver 761 (see FIG. 2) is configured to realize these four types of fixing speeds.

The conveying speed of the sheet conveying section 9g is set to be equal to the peripheral speed of the fixing upper / lower rollers 9a and 9b. In addition, the fixing speed V for two sides
The FD is used for the second surface of both sides for fixing toners of two or more colors. The FD is not used in the single color mode in which only one color toner is fixed on the second surface of both surfaces. In this case, the fixing operation is performed at a normal paper fixing speed VFN.

Next, a configuration for adsorbing the sheet material fed from each sheet material cassette 7 to the transfer drum 5a will be described with reference to FIGS. still,
FIG. 10 is an enlarged schematic diagram of a configuration of a D1 part in FIG.
FIG. 11 is a schematic diagram of a configuration including the transport path H on the upstream side of the transfer drum 5a.

The sheet material is conveyed along the conveyance path H, and enters the registration means 60 by the guide plates 61, 62, 63 and 64. The registration means 60 is composed of a registration roller 65 as a roller pair, and two rollers of two opposed rollers 66 and 67 which are opposed to and pressed against the registration roller 65.

The hardness of the two opposing rollers 66, 67 (for example, the opposing rollers 66, 67 are made of rubber-like elastic material (hard sponge) having a lower hardness than the registration roller 65, and come into contact with the outer peripheral surface of the registration roller 65. The position of the sheet material (the nip portion) is made concave, and the angle of entry of the registration roller 65 and the opposing roller 66 from the guide plates 63 and 64 into the nip portion is determined by the registration means 60.
When passing through, a curl that is convex to the right in the figure is formed.

Reference numerals 68 and 69 denote sheet material detection sensors for detecting a sheet material entering the registration means 60, for generating the drive control timing of the registration means 60 and detecting the conveyed sheet material (including an OHP sheet or the like). It is possible.

Therefore, the sheet material is adjusted in posture by the registration means 60 and the suction timing to the transfer drum 5a is adjusted, and the sheet material is curled along the outer peripheral shape of the cylindrical transfer drum 5a, and is suctioned by the suction roller 5g. An auxiliary operation is performed.

(Specific Example of Image Forming) As a specific example, four colors of plain paper (sheet material) in the "single-single mode" in which the automatic document feeder RDF400 is not used and the thick paper mode is not set are used. The image forming operation will be described.

In this case, since the sheet material on which the image is formed is plain paper, the speed setting for the fixing drive motor driver 761 is set to be the same VFN as the image forming speed (process speed) VP of the photosensitive drum 1. I do. After the operator sets the number of images to be formed with the ten keys 351 and then selects a paper feed stage with the sheet material selection key 303 and instructs the start of the operation with the start key 354, the printer controller 701: a drive motor required for image formation, for example, The driving of the photosensitive drum driving motor, the fixing driving motor, the sheet feeding driving motor, and the main driving motor is instructed.

Next, after the driving states of the drive motors are stabilized, the designated paper feed stage (sheet material cassette 7
a, 7b, etc.), the sheet feeding operation is started. At this time, at substantially the same time, the reader unit 201 converts the shift amount, the black extraction amount, the UCR amount, the reader color selection signal, and the like so that an image signal for magenta, which is the development color of the first color in the four-color mode, can be generated. This is set for each block of the image processing unit 203.

The reader gradation correction circuit 108 selects one of the conversion characteristics a to e shown in FIG. 4 corresponding to the contents specified by the manual density adjustment setting keys 304 and 305 of the operation unit 704. The conversion characteristic of m shown in FIG. 5 is selected for the printer gradation correction circuit 109.

The sheet material fed from the designated paper feed stage is transferred to the transfer drum 5 by the registration means 60 so as to be synchronized with the optical scanning operation of the reader unit 201.
sent to a.

At this time, the registration means 60 has a built-in curling function as shown in FIG.
The sheet material is formed into a curl along the transfer drum 5a so that the sheet material adsorbs the sheet material a. Hereinafter, a portion related to the curling function of the resist unit 60 is referred to as a curling unit 70.

As shown in FIG. 11, all the sheet materials pass through the curling portion 70 and are attracted to the transfer drum 5a. An image can be formed by feeding a paper from a cassette.

The sheet material is attracted to the transfer sheet 5f by the attraction charger 5c and the attraction roller 5g, which is an opposite electrode. As a pre-process of the suction operation, the transfer sheet 5f is neutralized by using the inner charger 5d and the outer charger 5e to eliminate the charge. AC + DC can be output to the inner charger 5d, and only AC can be output to the outer charger 5e.
Are supported to be in antiphase.

The detailed timing of each control will be described below with reference to FIGS. 8, 9, and 12. FIG. 8 shows the photosensitive drum 1 and the transfer drum 5a at the time of starting the latent image writing.
7 shows the positional relationship between the sheet material and the sheet material that has been adsorbed, and shows the state of single-sheet A-side adsorption in which the sheet material is adsorbed from the fixed point PTA on the transfer drum 5a.

In this embodiment, since a full-color image is formed in the order of magenta, cyan, yellow, and black, for example, when the transfer of magenta is completed and the start of writing the cyan latent image on the photosensitive drum 1 is started. It is a state of
From now on, the distance L from the laser writing position to the transfer position
After a lapse of L at the process speed VP, the transfer operation of cyan is started.

Next, FIG. 9 is a timing chart showing the situation in FIG. 8, and shows the relationship between the transfer drum reference signal, which is the basis of the timing control in this embodiment, and each image forming operation. Things.

From the fall of the transfer drum reference signal A to T
The optical motor driver 702 is set so that a latent image can be formed after the pri time, and a transfer drum reference signal C, which is a timing reference signal for a transfer operation performed after a distance LL from the start timing of the latent image, is prepared. ing. The transfer drum reference signal C is configured to rise before the transfer operation, that is, Tprei time before the sheet material transfer position passing section (time), and is a conventional transfer drum reference signal A for image formation (signal B in this example). The same applies to the case where the operation timing is generated, and more accurate timing control can be performed particularly when the image forming speed is changed.

Next, in order to make it easier to understand the detailed timing explanation, the distance relationship between the respective elements of the image forming operation in this embodiment will be described with reference to FIG.

As described above, the distance LLT from the laser writing position to the transfer position, the distance LAT from the suction position to the transfer position, the LTS from the transfer position to the separation position, and the distance LTC from the transfer position to the tip of the sheet conveying section 9g are LTC. = 25
0 mm, the distance LTD from the transfer position to the outer charger, and the distance LTCLN from the transfer position to the fur brush 14 for cleaning the transfer drum = 250 mm.

FIG. 13 shows timings required for image formation in terms of timing with respect to a sheet material so that the arrangement of control parts can be ignored. The image is output from the sheet material with the leading end and the trailing end missing 6 mm and 4 mm, respectively, and is represented as an effective image area in the figure.

This is necessary to prevent the inside of the apparatus from being stained due to toner falling during the period from transfer to fixing. The transfer high voltage required for the transfer operation rises at the leading end margin of 6 mm at the leading end of the sheet material, and falls at the rear end side in a portion exceeding the entire area of the sheet material. A DC output area of the inner charger, which operates only before suction, is secured outside the effective area of the transfer high voltage. This is because the transfer sheet 5f
Is set to a predetermined value before transfer.

Outside the DC area of the inner charger, a suction high-pressure area used for suctioning the sheet material is secured, and outside the area, the AC operation of the inner charger and the outer charger is performed to remove the charge from the transfer sheet 5f. There is an effective area.

If these timing relationships are not achieved, the desired transfer performance and sheet material transportability cannot be achieved. Therefore, the following configuration is used to secure a timing generation signal so as to guarantee the respective relationships. .

FIG. 14 is a block diagram of the high voltage control section 770 for realizing such timing. As an example, a transfer high voltage at which control timing is strict will be described.

Reference numeral 801 denotes a high-voltage transformer for generating a transfer current. Reference numeral 804 denotes a high-voltage transformer 801 using a high-voltage control signal (voltage) set by the D / A unit 753 as a reference.
An operation amplifier 805 controls the current flowing to the secondary side by controlling the current flowing to the primary side, and 805 is a current detecting resistor.

Next, referring to FIG. 15, high voltage control signal CTL-
V will be described. Since the transfer sheet 5f is a high-resistance body, the current required for transfer is very small.
Is a dielectric and therefore has some capacitance. Since a very small amount of current flows through the transfer sheet 5f of a high-resistance body having this capacitance, most of the current that flows at the beginning of the rise of the transfer current becomes a charging current for the capacitance, which is necessary for actual transfer. There is a slight delay before the start of the flow of the effective transfer current. To prevent this, FIG.
As shown in the figure, the acceleration current in which the charge current is superimposed at the time of the rise of the transfer current is flowing.

FIG. 15 shows a case where the conventional acceleration current control is not performed and a case where the conventional acceleration current control is performed. When the acceleration current control is not performed, the effective transfer current It necessary for the transfer is realized in the middle of the image area. On the other hand, in the present embodiment, the high-voltage control signal CTL-V is initially set to the setting value VctlA for the acceleration current, and is set to the setting value Vctl for the necessary effective transfer current It in the middle of the leading edge margin. The control is performed so as to guarantee the necessary effective transfer current It for the effective image area.

In this embodiment, the rising edge of the transfer drum reference signal A is used as the timing reference for the suction operation (B
The fall of the transfer drum reference signal B is used at the time of surface adsorption), and the fall of the transfer drum reference signal C is used for high voltage control of AC or DC of the inner charger and the outer charger. The sensor and the sensor light shielding flag are positioned so that the reference signal is generated a predetermined time before each operation. With this configuration, it is possible to control at an accurate timing even when an image forming speed described later is changed.

The timing control will be described with reference to FIG. FIG. 16 shows FIG. 9 in more detail. In the present embodiment, the rise of the transfer drum reference signal C is used for transfer control as described above. The transfer drum reference signal C rises before the transfer operation, that is, Tpret before the transfer time of the leading edge of the sheet material, and in this control, the drum motor clock, which is an encoder pulse output from the photosensitive drum motor driver 760 from this rise, is Tt1. That is, Lt1 is counted from the transfer drum reference signal projection position on the transfer drum to the acceleration current setting position in the middle of the leading edge margin, and the acceleration current setting value Vctl is calculated.
A is output. Thus, even when the speed of the motor is changing, the acceleration control can be accurately started at a desired position in the middle of the leading edge margin on the sheet material.

Next, the acceleration setting end time Tt2 is counted by the system clock counting function which is a built-in function of the printer controller 701 from the acceleration control start setting. This is because the acceleration setting effective period mainly depends on the environmental characteristics of the transfer sheet 5f and the environmental characteristics of the sheet material, and does not depend on the image forming speed. By this control, a desired effective transfer current can be secured for the image area.

The acceleration current set value VctlA
The acceleration setting end time Tt2 is optimally controlled according to the sheet material type, the temperature sensor 783, the humidity sensor 784, the number of transfers, ie, the transfer color, and the operation mode for one side, both sides first side, and both sides second side.

Further, as compared with the case where the measurement of the acceleration control start time Tt1 and the acceleration setting end time Tt2 is counted by using only the drum motor clock or the system clock, the control when the image forming speed is changed becomes more accurate. Needless to say, no adjusting means is required.

The document information read by the reader unit 201 is processed by the image processing unit 203,
Is irradiated as a laser beam on the photosensitive drum 1 uniformly charged by a laser beam to form a latent image.
Is developed. The developed image information is transferred by the transfer charger 5b onto the sheet material P adsorbed earlier. The image forming operations of M (magenta) document reading, latent image formation, development, and transfer are performed while the photosensitive drum 1 and the transfer drum 5a make one rotation, and similarly, C (cyan), The process is also performed for each color of Y (yellow) and Bk (black). At this time, the image processing unit 20
The setting for 3 is performed for each image formation.

The sheet material P on which the four color images are transferred is separated from the transfer sheet 5f. At this time, the separating sheet charger 5h reduces the attraction force between the transfer sheet 5f and the sheet material P, the transfer sheet 5f is deformed by the separation push-up roller 8b to perform curvature separation, and the separation claw 8a separates the transfer sheet 5f from the transfer sheet 5f. To separate.

The sheet material P thus separated is conveyed to the heat roller fixing unit 9 by the sheet conveying portion 9g which conveys at the same speed (VP) as the transfer drum 5a, and the fixing speed VFN = VP After the sheet is fixed in the above-described manner, the sheet is subjected to curl correction by the sheet discharge curl correction unit 500 and then discharged to the sorter 600.

Next, the control for the oil cleaning member will be described in detail. Since the control method of the oil cleaning control differs depending on the fixing speed, the oil cleaning control on plain paper will be described first.

First, control when the oil cleaning member is not operated in the plain paper mode (control when oil cleaning is not performed) will be described, and then control when the oil cleaning member is operated in the plain paper mode (oil control). The control during cleaning will be described.

(Control for Implementing No Oil Cleaning in Plain Paper Mode) FIG. 17 shows the start of the transfer operation of the final color to the final sheet (the last of a plurality of sheet materials on which the same original image is formed). 5 is a flowchart showing the control from the start to the stop of the image forming operation, and such control is usually called “post-rotation control”. Thereafter, by the rotation control, "normal cleaning control" of the transfer drum 5a, which is a sheet material holding unit, is executed. The normal cleaning control is a normal cleaning control using the fur brush 14 and the fur backup brush 15 as described later.

FIG. 18 is a timing chart when the single-sheet sticking control is performed by the "fixing (N) rotation control" described later when the transfer drum 5a has the two-sheet sticking controllable size in the flowchart of FIG. FIG. 19 is a flowchart of the “fixing (N +
5 is a timing chart when one-sheet sticking control or two-sheet sticking control is performed by “1) Rotation control”.

In the post-rotation control flowchart of FIG. 17, when the transfer of the final color of the image forming color determined by the color mode is started (step S1000), first,
It is determined whether the sheet is the last sheet material for the same document, that is, the last sheet (step S1001). Thus, after the transfer is completed, it is determined whether to perform the post-rotation control.

Image formation on the final sheet material (hereinafter referred to as
If it is not “final image formation”), the image forming operation is continued (step S1002), and this control ends (step S1003).

If the final image is to be formed, the size of the sheet in the transport direction is compared with the distance LTCLN from the transfer position to the transfer sheet cleaning position (step S100).
4). This is because the sheet material is applied to both the transfer position and the transfer sheet cleaning position (in the present embodiment, the distance LTCLN from the transfer position to the transfer sheet cleaning position is 250 m).
m), in order to prevent the occurrence of image disturbance if the cleaning operation of the transfer drum 5a or the separating operation of the sheet material is performed during the transfer to the sheet material, the sheet material is provided at both the transfer position and the transfer sheet cleaning position. In such a case, after the transfer drum 5a is idlely rotated by one rotation to end the transfer operation (step S1005), the separating operation (step S1006) and the cleaning operation (step S1008) are performed.

In the normal cleaning control in step S1007, the fur brush 14 is rotated by a motor (not shown), the fur backup brush 15 facing the fur brush 14 is enabled, and the fur brush 14 contacts the transfer sheet 5f. You only need to make contact. At this time, the transfer sheet 5f for one round of the transfer drum 5a is cleaned and the transfer sheet 5f
End the cleaning operation (step S1009). Thereafter, the load and high pressure of the operating motor and the like are stopped (step S1009), and the image forming operation is terminated (step S1).
010).

(Control for Performing Oil Cleaning in Plain Paper Mode) When forming a single-color image on both sides of plain paper, the image is formed on the second side of both sides (hereinafter referred to as “plain paper single-color double-sided two sides”).
), An oil cleaning operation of the transfer sheet 5f is performed as follows.

The sheet material fed from one of the cassettes and having an image formed on the first side is temporarily stored in the intermediate tray 22 and then fed again. The re-fed sheet material is carried on the transfer drum 5a for image formation on the second side. At this time, the surface of the transfer sheet 5f of the sheet material is in contact with the first image forming surface of the sheet material, and the oil adhered in the fixing device 9 at the time of forming the first image re-adheres to the surface of the transfer sheet 5f. Will be.

It is necessary to prevent the oil from adhering to the photosensitive drum 1. For this purpose, when the transfer sheet 5f during image formation on the second side of both surfaces passes the transfer position, it passes through the transfer position. The back surface of the transfer sheet 5f must be oil-cleaned in advance, or control must be performed so that a sheet material exists between the transfer sheet 5f and the photosensitive drum 1.

When the fixing speed is the same as the process speed at the time of two sides of single-color plain paper, the transfer sheet 5 is located at the transfer position when images are continuously formed on a plurality of sheet materials.
Since the sheet material is always present between f and the photosensitive drum 1, for example, it is sufficient to perform oil cleaning only during the post-rotation control described above.

By the way, the sheet material for forming the image on the second side of both sides may be supplied from the intermediate tray 22 or supplied from the sheet material tray 7m. In some cases, the user may reset the sheet material on which the image has been formed on the sheet material tray 7m in order to output a two-sided image. In this case, like the sheet feeding from the intermediate tray 22,
The control is performed on the assumption that there is a sheet material for the second surface on both sides on which an image is formed on the first surface.

Next, specific oil cleaning control will be described with reference to the flowchart of FIG. This FIG.
An example is shown in which oil cleaning and normal cleaning are performed at the time of face-up, and only normal cleaning is performed at other times.

The transfer drum cleaning starts (step S150).
0) If the sheet feeding position is the intermediate tray 22 or the sheet material tray 7m, it is determined in step S1501 that image formation is to be performed on the second side of both sides, and the oil cleaning backup brush 17 is used to perform an oil cleaning operation. Enable (step S1502), and drive the oil cleaning roller 16 to contact the transfer sheet 5f (step S1).
503).

Since the oil cleaning roller 16 is made of a material that absorbs oil, it comes into contact with the transfer sheet 5f to remove the oil adhering to the transfer sheet 5f. Next, in order to perform normal cleaning, the fur backup brush 15 is enabled (step S1504),
The fur brush 14 is driven and brought into contact with the transfer sheet 5f (step S1505), and the cleaning operation ends (step S1506). If the sheet feeding position is not the intermediate tray 22 or the sheet material tray 7m in step S1501, oil cleaning is not required, and only the fur brush 14 is driven to perform normal cleaning control (steps S1504 and S1505).

Incidentally, steps S1500 to S1500 in FIG.
When S1506 is executed in the transfer drum cleaning control (step S1007) in FIG. 17, oil cleaning can be performed as needed in post-rotation control.
Steps S1500 to S1506 in FIG.
7, the oil cleaning and the normal cleaning can be performed as needed each time the sheet material is separated from the transfer drum 5a.

Further, steps SS1500 to SS1500 in FIG.
When step S1503 is performed between step S1001 and step S1002 in FIG. 17, only oil cleaning can be performed as necessary each time the sheet material is separated from the transfer drum 5a.

(Specialty of resist curl control in thick paper mode) In order to make thick paper adhere to the transfer drum 5a, the present invention is achieved by changing the control of the resist means 60 to plain paper. The details are described below. In order to ensure the absorption quality of thick paper, it is necessary to increase the amount of curl at the leading end relative to other parts.
It has been confirmed by experiments.

FIG. 21 shows the drive timing of the registration means 60 for thick paper so that plain paper and thick paper can be compared.

In the case of a sheet material such as 150 g / m 2 (gram / square meter) in the case of the thick paper, the sheet material detecting sensor 68 is used so that the curling function of the sheet material functions more effectively. , 69, and after a lapse of time T401 in which the leading end reaches the opposing roller 66, the registration means 60 is moved to a time T4 in which the leading end of the sheet material engages the nip portion between the resist roller 65 and the opposing roller 67.
Drive by 02.

Since the leading end of the sheet material at the time of thick paper is ahead of the case of plain paper by the distance of the facing roller 66 by the facing roller 67, the drive timing for attracting the transfer drum 5a to the transfer drum 5a is determined by T402 from the timing of plain paper. It is controlled to drive with only a delay.

The time T403 during which the tip curl becomes effective is
By adjusting the paper feed timing appropriately, it becomes possible to adjust the amount of curl required for the sheet material.
Sheet materials having a wider range of thickness can be adsorbed.

It should be noted that such control need not be performed for plain paper in which the curling of the sheet material tip does not significantly affect the attraction to the transfer sheet 5f.

(Speciality of fixing speed in thick paper mode)
Fixing toner on thick paper requires more energy than plain paper, so the fixing speed is slower than plain paper, and the energy per unit area / hour The fixability of is secured.

In this case, conventionally, the distance from the separation claw 8a to the contact position of the fixing upper / rollers 9a and 9b is made larger than the maximum size of the thick paper capable of forming an image, so that the image forming speed (process speed) VP is increased. While the peripheral speed of a certain transfer drum 5a is kept constant, the sheet material is reduced to a fixing speed VF different from the speed of the transfer drum 5a in the sheet material transport section 9g, and the sheet material transport section 9g is used as a speed conversion area. I was using. For this purpose, it is necessary to secure a sheet material conveying section 9g having a size corresponding to the maximum size of a thick paper on which an image can be formed.

Therefore, in the present embodiment, the transfer drum 5
When the fixing speed VF must be lower than the image forming speed VP, the transfer of the final color is completed.
The speed of the transfer drum 5a is reduced to the fixing speed. This eliminates the need to secure a size as a speed conversion area in the sheet material transporting section 9g, thereby avoiding an increase in the size of the apparatus.

When the size of the sheet in the conveying direction is larger than the distance LTC from the transfer position in FIG. 1 to the leading end of the sheet conveying section 9g, the transfer drum 5
The deceleration to the fixing speed a does not meet the timing of the next sheet material separating operation. In such a case, the transfer drum 5a is rotated one extra turn, and the sheet material separating operation is performed at the timing of the subsequent separating operation.

As described above, after the transfer of the final color in the thick paper mode is completed, the transfer drum 5a is rotated one more revolution, the separation operation is performed, and the control for further fixing is hereinafter referred to as "fixed thick paper (N + 1) rotation control". . In addition, the control is performed when the distance LTC from the transfer position to the leading end position of the sheet material conveyance unit 9g or when the sheet material conveyance unit 9g can be used as a speed conversion area, that is, when it is not necessary to rotate the transfer drum 5a one extra rotation. Hereinafter, it is referred to as “fixing thick paper (N) rotation control”.

Here, to make the explanation easy to understand,
Assuming that the distance LTC from the transfer position in FIG. 1 to the leading end position of the sheet material conveying section 9g is 250 mm, the following control is performed in the thick paper mode based on the typical sheet material size.

A4 horizontal feed size (210 mm in feed direction)
One-sheet application: Fixing thick paper (N) rotation control A4 vertical feed size (297 mm in feed direction) One-sheet application: Fixing thick paper (N + 1) rotation control A3-longitudinal feed size (420 mm in feed direction) One-sheet application: Fixing thick paper (N + 1) rotation Control A4 horizontal feed size (feed direction 210 mm) 2 sheets stuck: fixed thick paper (N + 1) rotation control.

(Speciality of Oil Cleaning in Thick Paper Mode) Next, oil cleaning control in the thick paper mode in which the fixing speed needs to be slowed down will be described. As described above, in the case of the oil cleaning control of plain paper, since the speed of the transfer drum 5a is not changed after the image formation on the transfer drum 5a, the image forming operation can be continuously performed. It only needs to be performed at the end of the image forming operation on the last sheet of the document.

On the other hand, in the thick paper mode, the speed of the transfer drum 5a and the photosensitive drum 1 is set to the same speed as the fixing speed VFT for fixing control. And the photosensitive drum 1 must be returned to the original speed VP again. If the sheet material is different, a continuous image forming operation cannot be performed. Therefore, when an image is formed on the second side of the thick paper, the adhered oil on the transfer sheet 5f adheres to the photosensitive drum 1 at the transfer position, and the transfer operation of the final color to each sheet material ends. Each time requires oil cleaning control. Therefore, when an image is formed in the thick paper mode, the oil cleaning control is performed every time the transfer operation of the final color to each sheet material is completed as described below.

(Control of Forming Image in Thick Paper Mode) The control of forming a color image in the thick paper mode will be described below with reference to the flowchart of FIG. The flowchart of FIG. 22 corresponds to all sheet materials in the thick paper mode, the plain paper mode, and the OHP mode. Therefore, in FIG. 22, the control corresponding to the fixing thick paper (N + 1) rotation control and the control corresponding to the fixing thick paper (N) rotation control are defined as fixing (N + 1) rotation control and fixing (N) rotation control, which are common to all sheet materials. It is expressed as

As described above, the latent image including sheet feeding and suction,
The development and transfer operations (step S2000) are repeated until the final color is transferred (step S2001). After the transfer of the final color, the fixing speed VF and the image forming speed VP are compared (step S2002). Here, in the case of the thick paper mode, since the fixing speed VF is the slow fixing speed VFT for the thick paper and the fixing speed VF is different from the image forming speed VP, the process proceeds from step S2002 to step S2003.

In the step S2003, the transfer sheet 5f
It is determined whether the mode is a mode for holding a plurality of sheet materials. In the present embodiment, since the electrostatic attraction is used as the sheet material holding means, the entire circumference of the transfer sheet 5f is set to one.
In the case of a sheet material of / 2 or less, an image can be formed simultaneously on two sheet materials. In this example, when images are simultaneously formed on two sheet materials (two sheets are adhered),
In order to treat one sheet material as one sheet material including the distance between the sheets, the leading end position of the sheet material transport unit 9g from the transfer position is smaller than the size of the sheet material transport direction treated as one sheet material. Is small, and the distance L from the transfer position to the leading end position of the sheet material conveying unit 9g is reduced.
It is assumed that TC cannot be used as a speed conversion area. Therefore, in this case, “fixing (N + 1) rotation control” is performed (step S2006).

Next, when an image forming operation is performed with only one sheet material carried on the transfer sheet 5f (single sheet sticking), the distance L from the transfer position to the leading end position of the sheet material transporting section 9g is determined.
A comparison is made between TC and the size PX of the sheet material in the sheet material conveyance direction (step S2004). The size PX is the distance L
If it is larger than TC, the distance from the transfer position to the leading end position of the sheet material conveyance unit 9g cannot be used as a conversion region of the fixing speed, so that “fixing (N + 1) rotation control” is performed (step S2006). Conversely, if the size PX is smaller than the distance LTC (step S20)
04), “Fixing (N) rotation control” is performed (step S2)
005).

In this example, the distance LTC is compared with the size of the sheet material in the transport direction. If the speed change takes time due to the performance of the drum motor, the time required for the speed change is taken into consideration. Judgment step (Step S2
003, step S2004) can be improved. Further, in the fixing (N) rotation control, when the transfer sheet 5f is cleaned substantially simultaneously with the sheet material separating operation, the cleaning operation of the transfer sheet 5f may have an adverse effect on the sheet material during transfer. It is necessary to change the control depending on the size in the sheet material conveyance direction and the distance from the transfer position to the transfer sheet cleaning position. In this embodiment, the distance LTC and the distance LTCLN from the transfer position to the transfer sheet cleaning position are each set to be equal to 250 mm.

(Fixing (N) rotation control in thick paper mode) Hereinafter, the fixing (N) rotation control in the thick paper mode will be described with reference to the timing chart of FIG. In FIG. 23, K means a black image, and indicates a period from the time of forming the black image, which is the final color of the four-color operation, to the time of the transfer drum cleaning operation.

In this example, a single A-side A4-size paper sheet is used, and the latent image formation start timing T1200 is set at Tp.
The timing T1201 is generated from the falling timing T1201 of the transfer drum reference signal A before the rei time.
After a predetermined timing, the driving of the optical system is started. At timing T1200, control is performed so that the original can be read.

After a developing operation (not shown), a transfer start timing T1202 is reached after a lapse of the distance LLT at the process speed VP from the latent image start timing T1200, and the transfer operation is started. At this time, in order to achieve the accuracy of the transfer high voltage control, the transfer high voltage is controlled from the rising edge of the transfer reference position signal C output a predetermined distance before the transfer position (T12).
04).

At the end of the transfer operation for the sheet material size (T1
In step 203), a VFT for the fixing speed is set for the photosensitive drum motor driver 760. When the leading edge of the sheet material reaches the separation position before or after this (T1205)
Then, the separating operation is started to separate the sheet material to the fixing device 9 side. Transfer sheet 5 that has been separated and has no sheet material adsorbed
By counting the drum clock, which is the encoder output of the photosensitive drum motor, from the separation start timing T1205 with respect to f, including the speed change area of the drum motor,
The cleaning start timing T1206 of the transfer sheet 5f is detected, and the cleaning operation is performed.

Fixing (N) rotation control (step S200)
The operation 5) starts after the start of the final color transfer (step S2001). The separating operation is the same as in the case of the plain paper mode which is not the thick paper mode. That is, it waits until the separation operation start timing T1205, and when the separation start timing comes, the separation claw 8a and the separation push-up roller 8b are operated to start the separation operation.

Next, the process waits until the transfer end timing T1208, which is determined from the size PX of the sheet in the conveying direction, is reached. When the transfer end timing comes, the output of the transfer charger is set to OFF, and the photosensitive drum motor driver 7 is turned off.
For 60, the peripheral speed of the transfer drum 5a is set to be the same as the fixing speed VFT for thick paper. afterwards,
Wait until the separation operation end timing T1207, and turn off the separation claw 8a to end the separation operation.

When such transfer is performed on the second side of both sides in the thick paper mode, as described above, the fixing oil of the first side of the sheet material adheres to the surface of the transfer sheet 5f after separation. Therefore, step S20 in FIG.
At 08, it is determined that oil cleaning is necessary, and oil cleaning control is performed before the area of the transfer sheet 5f to which the fixing oil has adhered reaches the transfer position again (step S200).
9). The oil cleaning is performed in step S in FIG.
Similarly to 1502 and S1503, the control is such that the oil cleaning backup brush 17 is activated and the oil cleaning roller 16 is driven to abut the transfer sheet 5f. After all,
At the time of the second side of both sides in the thick paper mode, oil cleaning control is performed every time the sheet material is separated.

Before the leading edge of the sheet reaches the sheet conveying section 9g driven at the fixing speed VFT for thick paper, the peripheral speed of the transfer drum 5a is adjusted to the fixing speed VFT.
It becomes the same as T, the sheet material is separated and transported normally,
Fixing is performed at a fixing speed VFT for thick paper. Then, after waiting for the sheet material to be discharged (step S201)
0) In order to form an image on the next sheet material, the speed of the transfer drum 5a determined by the speed of the drum motor is set to the speed VP for image formation (step S2011).

After performing the above operation for the set number of sheets (step S2012), the image forming operation is completed.

(Fixing (N + 1) rotation control in thick paper mode) Hereinafter, the fixing (N + 1) rotation control in the thick paper mode will be described with reference to the timing chart of FIG. FIG.
4 is an example when two sheets are stuck, and in FIG.
K2 corresponds to the black image for the second sheet material, and K2 corresponds to the black image for the second sheet material. Sheet material for K1 is fixed point PTB
, And the sheet material for K2 is controlled to be sucked from the fixed point PTA.

In the fixing (N + 1) rotation control, as described above, the size of the sheet in the conveying direction is larger than the distance LTC (= 250 mm) from the transfer position to the leading end of the sheet conveying section, and the distance between these is determined by the fixing speed. When it cannot be used as the speed conversion area, after the end of the transfer operation,
The separation operation is performed after the transfer drum 5a is rotated once, and the separation operation is performed at the same time during the two-sheet bonding control. Therefore, the size of the combined sheet material including the sheet material interval becomes larger than LTC. The main fixing (N + 1) rotation control is executed.

Therefore, the process waits until T1300 is reached at the end of the transfer of the final color on the second sheet of the two sheets pasted, and at the end of transfer T1300, the high voltage of the transfer charger is turned off to perform the transfer operation. To end. Next, the peripheral speed of the transfer drum 5a is set to be equal to the fixing speed VFT for thick paper, and the fixing speed VFT is waited until the separation start timing T1301 in the next rotation is reached. At the separation start timing T1301, the separation operation is performed, and after the separation operation is completed, the separation claw 8a is turned off.
F, and the operation ends.

During this time, the sheet material passes through the transfer position. At this time, control is performed so that a transfer high voltage for preventing re-transfer is output so that the toner transferred to the sheet material is not re-transferred to the photosensitive drum 1 again. are doing. At this time, since the speed of the transfer drum is changing, the output timing control of the transfer high voltage is performed based on the transfer reference signal C (T1302, T1303) described above. In this control method, the timing controllability is remarkably improved as compared with the method of controlling the transfer high voltage based on the transfer drum reference signals A and B conventionally configured for image formation.

When such transfer is performed on the second side of both sides in the thick paper mode, as described above, the fixing oil of the first side of the sheet material adheres to the surface of the transfer sheet 5f after separation. Therefore, step S20 in FIG.
At 08, it is determined that oil cleaning is necessary, and oil cleaning control is performed before the area of the transfer sheet 5f to which the fixing oil has adhered reaches the transfer position again (step S2).
009). After all, at the time of the second side of both sides in the fixing (N + 1) rotation control in the thick paper mode, the oil cleaning control is performed every time the sheet material is separated.

As described above, the speed conversion area is formed by the extra rotation of the transfer drum 5a, and the fixing operation in the thick paper mode for the sheet material up to the maximum image forming size in the normal operation is performed. Becomes possible. Also,
The thick paper mode can be realized even by the operation of attaching two sheets.

After waiting for the completion of the separation of the sheet material (step S2010), the speed of the transfer drum 5a is set to the image forming speed VP for forming an image on the next sheet material (step S2011). This is because, in the present embodiment, the sheet material conveyance section 9g is driven by the fixing motor, and the effective area of the transfer drum speed for the sheet material is the end of the separation operation. It returns to VP which is the forming speed (T1304).

After performing such operations for the set number of sheets (step S2012), the image forming operation is completed.

(Fixing Normal Rotation Control in Plain Paper Mode) In the case of the plain paper mode with respect to the above-described thick paper mode, since the image forming speed VP and the fixing speed are equal, FIG.
The process proceeds from step S2002 of step 2 to step S2007 to perform "fixing normal rotation control" (step S200).
7). In the fixing normal rotation control, since the fixing speed is equal to the image forming speed VP, the image is continuously formed on the transfer sheet 5f. (Steps S2013 to S2015).

For plain paper, when it is determined that oil cleaning is necessary in step S2014 after forming a set number of images, oil cleaning control is performed (step S2015).
Is performed, and then the control is terminated. As described above, it is determined that the oil cleaning is necessary for the second side of both sides fed from the intermediate tray 22 or the sheet material tray 7m.

In the recording mode (OHP mode) for an OHP sheet having a different fixing speed from the thick paper mode, if the fixing speed is set to VFO, application to an OHP sheet material is possible as in the case of thick paper. is there. If the second side of both sides is not in the single color mode, the fixing speed VFD is different from the process speed VP, so that the same oil cleaning control as that of the second side of both sides of the thick paper mode may be performed.

In consideration of the effect of the toner or the like adhering to the first side of the sheet material when fixing the second side, the fixing speed may be controlled to be slower for the second side than for the first side. Such control can be performed regardless of the plain paper mode, the thick paper mode, or the OHP mode.

(Recovery Control) Next, recovery control after a paper jam detection (hereinafter, abbreviated as “jam detection”) in the image forming apparatus realized as described above will be described with reference to a flowchart of FIG. When a jam occurs as is well known (step S3000), the conveyance of the sheet material is stopped, and the occurrence of the jam is displayed on the operation unit (step S3001).

Thereafter, if the door opened to remove the jammed sheet material is opened and closed (step S300).
2, S3003), it is confirmed whether or not the sheet material is removed from the sheet material conveyance path or the transfer drum by a sheet material conveyance sensor (not shown) (step S3004). When the removed sheet material includes the sheet material of the second surface on both sides, the fixing oil on the image formed on the first surface of the sheet material adheres to the surface of the transfer sheet 5f when stopped. . Therefore, in this case, the process proceeds from step S3005 to step S3006, where the oil cleaning control is performed and the cleaning operation of the transfer sheet 5f is performed.

On the other hand, if the sheet material of the second side of both sides is not included, the oil cleaning control is not performed and the fur brush 14
And the transfer sheet 5f is cleaned only by the fur backup brush 15 (step S3007).
Control is performed to perform a recovery operation (step S300)
8, step S3009, step S3010).

The determination in step S3005 may be a determination as to whether oil cleaning control is necessary. If a sheet jam that requires oil cleaning control is detected, oil cleaning control is performed before recovery control. Further, it is possible to prevent the fixing oil from adhering to the photosensitive drum 1 during the recovery control. In the present embodiment, since the presence or absence of the oil cleaning control is determined according to the fixing speed and the paper feeding place, the oil cleaning control before the recovery control can be performed in all cases by extending these determination conditions. Becomes

(Second Embodiment) In the first embodiment, the oil cleaning control is performed even in the OHP mode. However, the oil cleaning is not performed on the OHP sheet material in which it is difficult to form images on both sides. Is also possible.

(Third Embodiment) In the first embodiment, the conveying speed of the sheet conveying section 9g is the same as the fixing speed, but the conveying speed of the sheet conveying section 9g is adjusted to the transfer drum 5a. You may comprise so that it may become the same as a peripheral speed.

In this case, the distance LTC compared with the size PX of the sheet in the sheet conveying direction in the first embodiment can be realized by replacing it with the distance LTF from the transfer position to the fixing roller.

(Fourth Embodiment) In the first embodiment, the case of the four-color mode and the thick paper mode has been described.
This can be realized even in any of the color / two-color / three-color modes and the cardboard mode.

Further, in the case of the one-color mode in which the heat energy supplied to the sheet material per unit time may be relatively small and the thick paper mode, it is possible to output an image whose fixing property is guaranteed without lowering the fixing speed. In this case, the operation can be performed without lowering the fixing speed only in the one-color mode. In this case, the oil cleaning control may be realized by the same control as that for plain paper.

(Fifth Embodiment) In the first embodiment, the type of a sheet material is set using a setting key or the like. It is also possible to detect whether or not.

These sheet material detection sensors have a light emitting portion and a light receiving portion, and the passage between the light emitting portion and the light receiving portion is detected by shielding the light between the light emitting portion and the light receiving portion by the sheet material. OHP is, due to its configuration,
Since only the tip is shielded from light and is not shielded from the middle, OHP utilizing such characteristics is utilized.
Can be detected.

FIG. 26 shows an OHP used in the image forming apparatus of the present embodiment. In FIG. 26, S is a light-shielding band. As described above, by utilizing the characteristics of the OHP, the image forming control including the control of the curling amount based on the OHP detection can be automatically executed.

[0189]

As described above, appropriate curling control is performed according to the type of sheet material, such as the thickness and paper type.
It is possible to stably convey the sheet material and form a high-quality image.

That is, by controlling the sheet material stop position and the stop time in the roller pair for pinching and conveying the sheet material, the curling amount of the sheet material can be changed, and a complicated mechanism is not provided. The purpose is achieved with a configuration that suppresses the up.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional configuration explanatory view of a color image forming apparatus as an embodiment.

FIG. 2 is a block diagram of a control system of the color image forming apparatus of FIG.

FIG. 3 is a detailed control block diagram of an image processing unit shown in FIG. 2;

4 is a gradation correction characteristic diagram showing an example of an input / output signal in the reader gradation correction circuit of FIG.

5 is a gradation correction characteristic diagram showing an example of an input / output signal in the printer gradation correction circuit of FIG.

6 is a schematic plan view of the operation unit shown in FIG.

FIG. 7 shows a control for attaching one sheet to a transfer drum (FIG. 7)
FIG. 8A is an explanatory diagram of (a) and two-sheet sticking control (FIG. 7 (b)).

FIG. 8 is a diagram illustrating a positional relationship between a transfer drum and a photosensitive drum.

FIG. 9 is a timing chart for explaining a transfer reference signal.

FIG. 10 is a detailed cross-sectional configuration explanatory view around a curling portion.

FIG. 11 is an explanatory diagram of a configuration around a curling portion.

FIG. 12 is a diagram illustrating a distance relationship between image forming units illustrated in FIG. 1;

FIG. 13 is a timing chart illustrating high-pressure control timing for a sheet material.

FIG. 14 is a block diagram illustrating a high-pressure control unit.

FIG. 15 is a timing chart illustrating transfer control timing.

FIG. 16 is a timing chart illustrating transfer acceleration control.

FIG. 17 is a flowchart for explaining the operation from the start of the final color transfer operation on the final paper to the stop of the image formation operation in the color image forming apparatus shown in FIG. 1;

FIG. 18 is a flow chart of FIG.
It is a timing chart at the time of performing one-sheet sticking control by rotation control.

FIG. 19 is a flowchart for fixing (N +
1 is a control timing chart when one-sheet sticking control or two-sheet sticking control is performed by rotation control.

FIG. 20 is a flowchart illustrating a transfer drum cleaning operation applicable in the flowchart of FIG. 17;

FIG. 21 is a timing chart for explaining control of a curling unit at the time of conveying thick paper.

FIG. 22 is a flowchart illustrating fixing control in the color image forming apparatus of FIG. 1;

FIG. 23 is a timing chart for explaining a fixing (N) rotation operation in a thick paper mode in the flowchart of FIG. 22;

24 is a timing chart for explaining a fixing (N + 1) rotation operation in a thick paper mode in the flowchart of FIG. 22;

FIG. 25 is a flowchart for explaining processing when a jam occurs in the color image forming apparatus of FIG. 1;

FIG. 26 is a plan view of an OHP sheet material usable in the color image forming apparatus of FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 2 corona charger 3 laser exposure optical system 4 developing device 5 transfer device 5f transfer sheet 6 cleaning device 7 sheet material cassette 8a separation claw 8b separation push-up roller 9 heat roller fixing device 11 pre-exposure lamp 12 potential sensor 13 on drum Light amount detection sensor 14 Fur brush 15 Fur backup brush 16 Oil cleaning roller 17 Oil cleaning backup brush 18 Polishing roller 19 Transport path switching guide 201 Leader unit 202 Printer unit 203 Image processing unit PR1 Image forming apparatus

Claims (6)

[Claims] 1. A conveyance path for a sheet material, a pair of rollers capable of curling the sheet material by nipping and conveying the sheet material at a nip portion in the conveyance path, and control means for controlling the driving of the pair of rollers. A sheet conveying device, wherein the roller pair is temporarily stopped in a state where the leading end of the sheet member is held between the nip portions of the roller pair by the control means. 2. The control device according to claim 1, wherein the control unit abuts a leading end of the sheet material conveyed by a conveyance unit disposed upstream of the roller pair on a conveyance path against a nip portion of the stopped roller pair. 2. The sheet conveying apparatus according to claim 1, wherein after the skew correction is performed, the roller pair is driven to guide the sheet to the nip portion. 3. 3. The sheet conveying apparatus according to claim 2, wherein the control unit controls the timing of conveying the sheet to a downstream side of the pair of rollers in the conveying path. 4. A sheet material information input means for inputting sheet material type information as one of the control information of the control means, wherein the control means controls the pair of rollers according to the inputted sheet material type information. 4. The apparatus according to claim 1, wherein the control unit can selectively control whether to temporarily stop the roller pair in a state where the leading end of the sheet material is held in the nip portion.
The sheet material conveying device according to any one of the above. 5. A sheet material conveying device according to claim 1, further comprising: an image forming unit configured to form an image on the sheet material conveyed by the sheet material conveying device. Characteristic image forming apparatus. 6. The image forming means includes a holding means for electrostatically adsorbing the conveyed sheet material and supporting the conveyed sheet material on a surface thereof, and forming a toner image on the sheet material carried on the surface of the supporting means. The image forming apparatus according to claim 5, wherein: